Bioindicators and Ecological Assessment of Drigh Lake Water Quality: Physico-Chemical, Biological and Hydrological Characterization Under Anthropogenic Influences

Abstract

Background: Drigh Lake is a Ramsar-designated freshwater wetland in Sindh, Pakistan, increasingly exposed to anthropogenic nutrient and organic loading that may accelerate eutrophication and degrade ecological integrity. Objective: To integrate physico-chemical, hydrological, and multi-trophic bioindicator evidence to characterize water quality status and ecological condition of Drigh Lake under seasonal and human influence. Methods: A cross-sectional observational ecological assessment was conducted using monthly sampling from four fixed stations during 2010–2013. In situ and laboratory analyses followed standardized procedures for temperature, transparency, pH, total suspended solids (TSS), total dissolved solids (TDS), salinity, alkalinity, hardness, and dissolved oxygen. Biological assessment quantified seasonal plankton composition and documented macrophyte and fish assemblages as bioindicators of trophic state. Results: Water temperature ranged 14.0–35.0 °C (mean 24.7 ± 5.8), transparency 42–167 cm (85.4 ± 40.2), pH 6.2–8.9 (7.7 ± 0.8), TSS 16–44 mg L⁻¹ (28.2 ± 7.1), TDS 956–1294 mg L⁻¹ (1158 ± 102), salinity 0.4–4.8‰ (1.6 ± 1.1), alkalinity 142–389 mg L⁻¹ as CaCO₃ (215 ± 45), hardness 168–412 mg L⁻¹ as CaCO₃ (243 ± 62), and dissolved oxygen 6.2–9.7 mg L⁻¹ (7.8 ± 1.2). Phytoplankton were dominated by Cyanophyta, Chlorophyta, Euglenophyta, and Bacillariophyta, with eutrophy-associated genera (e.g., Microcystis, Oscillatoria) increasing in warm and post-monsoon seasons; zooplankton were primarily Rotifera, Copepoda, and Cladocera with marked seasonal restructuring. Proliferation of emergent, floating, and submerged macrophytes including Typha, Phragmites, Eichhornia, and Hydrilla supported a eutrophic classification and habitat alteration. Conclusion: Integrated chemical and bioindicator signals indicate Drigh Lake is a productive but eutrophic wetland under anthropogenic stress, warranting nutrient-load reduction, hydrological management, invasive macrophyte control, and sustained monitoring to restore ecological balance.